Disentangling the assembly mechanisms controlling community composition,structure,distribution,functions,and dynamics is a central issue in ecology.Although various approaches have been proposed to examine community a...Disentangling the assembly mechanisms controlling community composition,structure,distribution,functions,and dynamics is a central issue in ecology.Although various approaches have been proposed to examine community assembly mechanisms,quanti-tative characterization is challenging,particularly in microbial ecology.Here,we present a novel approach for quantitatively delineating community assembly mechanisms by combining the consumer–resource model with a neutral model in stochastic differential equations.Using time-series data from anaerobic bioreactors that target microbial 16S rRNA genes,we tested the applicability of three ecological models:the consumer–resource model,the neutral model,and the combined model.Our results revealed that model performances varied substantially as a function of population abundance and/or process conditions.The combined model performed best for abundant taxa in the treatment bioreactors where process conditions were manipulated.In contrast,the neutral model showed the best performance for rare taxa.Our analysis further indicated that immigration rates decreased with taxa abundance and com-petitions between taxa were strongly correlated with phylogeny,but within a certain phylogenetic distance only.The determinism underlying taxa and community dynamics were quantitatively assessed,showing greater determinism in the treatment bioreactors that aligned with the subsequent abnormal system functioning.Given its mechanistic basis,the framework developed here is expected to be potentially applicable beyond microbial ecology.展开更多
Context dependence arises when ecological relationships vary with the conditions under which they are observed. Context dependence of interactions involving parasites is poorly known, even if it is key to understandin...Context dependence arises when ecological relationships vary with the conditions under which they are observed. Context dependence of interactions involving parasites is poorly known, even if it is key to understanding host–parasite relationships and food web dynamics. This paper investigates to which extent predation pressure on an avian ectoparasite (Carnus hemapterus) is context-dependent. Based on a predator-exclusion experiment, predation pressure on C. hemapterus pupae in the host's nest for 3 years, and its variation between habitat types are quantified. Variation in precipitation and normalized difference vegetation index (NDVI) is also explored as a likely cause of context dependency. We hypothesize that predation pressure should fluctuate with such surrogates of food availability, so that inter-annual and intra-annual differences may emerge. The number of nests with significant reduction of pupae varied widely among years ranging from 24% to 75%. However, average pupae reduction in nests where a significant reduction occurred did not vary between years. No differences in predation rates between habitat types were detected. Precipitation and NDVI varied widely between years and NDVI was consistently lower around nests on cliffs than around nests on trees and farmhouses. Parallels were found between variation in predation pressure and precipitation/NDVI at a wide scale (highest predation the driest year, and much lower the 2 rainier ones), but not at the nest scale. This paper shows clear context-dependent insect predation pressure on an ectoparasite under natural conditions, and that such interaction changes in signs rather than magnitude between years. The causes for these variations require longer-term studies and/or well-designed, large-scale experiments.展开更多
文摘Disentangling the assembly mechanisms controlling community composition,structure,distribution,functions,and dynamics is a central issue in ecology.Although various approaches have been proposed to examine community assembly mechanisms,quanti-tative characterization is challenging,particularly in microbial ecology.Here,we present a novel approach for quantitatively delineating community assembly mechanisms by combining the consumer–resource model with a neutral model in stochastic differential equations.Using time-series data from anaerobic bioreactors that target microbial 16S rRNA genes,we tested the applicability of three ecological models:the consumer–resource model,the neutral model,and the combined model.Our results revealed that model performances varied substantially as a function of population abundance and/or process conditions.The combined model performed best for abundant taxa in the treatment bioreactors where process conditions were manipulated.In contrast,the neutral model showed the best performance for rare taxa.Our analysis further indicated that immigration rates decreased with taxa abundance and com-petitions between taxa were strongly correlated with phylogeny,but within a certain phylogenetic distance only.The determinism underlying taxa and community dynamics were quantitatively assessed,showing greater determinism in the treatment bioreactors that aligned with the subsequent abnormal system functioning.Given its mechanistic basis,the framework developed here is expected to be potentially applicable beyond microbial ecology.
文摘Context dependence arises when ecological relationships vary with the conditions under which they are observed. Context dependence of interactions involving parasites is poorly known, even if it is key to understanding host–parasite relationships and food web dynamics. This paper investigates to which extent predation pressure on an avian ectoparasite (Carnus hemapterus) is context-dependent. Based on a predator-exclusion experiment, predation pressure on C. hemapterus pupae in the host's nest for 3 years, and its variation between habitat types are quantified. Variation in precipitation and normalized difference vegetation index (NDVI) is also explored as a likely cause of context dependency. We hypothesize that predation pressure should fluctuate with such surrogates of food availability, so that inter-annual and intra-annual differences may emerge. The number of nests with significant reduction of pupae varied widely among years ranging from 24% to 75%. However, average pupae reduction in nests where a significant reduction occurred did not vary between years. No differences in predation rates between habitat types were detected. Precipitation and NDVI varied widely between years and NDVI was consistently lower around nests on cliffs than around nests on trees and farmhouses. Parallels were found between variation in predation pressure and precipitation/NDVI at a wide scale (highest predation the driest year, and much lower the 2 rainier ones), but not at the nest scale. This paper shows clear context-dependent insect predation pressure on an ectoparasite under natural conditions, and that such interaction changes in signs rather than magnitude between years. The causes for these variations require longer-term studies and/or well-designed, large-scale experiments.
